The present invention relates to an image forming apparatus, such as a digital copying machine, a facsimile device, and a scanner device, which binarizes an input image per pixel and subjects the image to a resolution conversion process or scaling process so as to output the input image.
In an image forming apparatus such as a digital copying machine and a scanner device, there is a case where an enlargement process or resolution conversion process is carried out with respect to an input image such as characters.
Conventionally, when carrying out a resolution conversion process or scaling process, it has been common practice to simply increase or reduce the number of pixels. The advantage of this practice is that the hardware is realized in a simple manner.
Namely, in a usual case, binary image data, that is, 1 bit image data, are expressed as shown in FIG. 26(a), and when outputting this data from a device such as a hard copy device, the data are outputted as shown in FIG. 26(b).
In order to simply double the size of the image, the image data of FIG. 26(b) are interpolated to have a data amount four times the original amount, and the interpolated data are outputted in the manner as shown in FIG. 26(c). In this case, the dot diameter of the hard copy device is reduced to half, and the dot density is increased four times.
When the dots printed by the hard copy device are of the same size as the ones shown in FIG. 26(c), an image of double the size of the original is outputted. Thus, whether the process is a resolution conversion or scaling is decided by the dot diameter of the hard copy device.
However, when the binary image of the input image is directly subjected to enlargement, etc., by this method, certain patterns, such as rough step-like edges of characters or stripes, are generated, and the resulting image is notably unsatisfactory in terms of image quality.
In order to solve this problem, in recent years, a process called smoothing is adopted to realize smooth displaying. An example of this process is the enlarged character pattern correcting method as disclosed in Japanese Unexamined Patent publication No. 172264/1988 (Tokukaisho 63-172264).
In this method, a standard character pattern is enlarged two times in the vertical and lateral directions, and as shown in FIG. 27(a) through FIG. 27(d), when a predetermined pattern of 3xc3x973 pixels is detected, a correction pattern is calculated by a certain equation.
However, in the conventional image forming apparatuses, the image is only enlarged two times in the vertical and lateral directions by the above method, and there is a problem that unrounded magnifications, i.e. magnifications in non-integral multiples, cannot be handled.
Also, the described resolution conversion process and scaling process have a proble that a notably unsatisfactory ugly pattern is generated when these methods are used on a half-tone image.
The present invention offers a solution to the above-mentioned problems, and accordingly it is an object of the present invention to provide an image forming apparatus capable of complying with unrounded magnifications of other than integral multiples, and also capable of reproducing a desirable image even with respect to a character image and a pseudo-halftone image.
In order to achieve the above object, an image forming apparatus of the present invention, which outputs a binary image by carrying out interpolation in a resolution conversion process or scaling process, includes an interpolation point calculating section for carrying out interpolation density and interpolation point in interpolation, and an offset section for giving an offset beforehand when the interpolation point calculating section calculates interpolation point.
In this image forming apparatus, interpolation is carried out by calculation of interpolation density and interpolation point by the interpolation point calculating section when subjecting a binary image to resolution conversion or scaling. Here, in calculation of interpolation density and interpolation point, the offset section gives an offset beforehand to the interpolation point calculating section.
This solves the problem of the conventional interpolation method that information of only one pixel is used for calculation of interpolation density and interpolation point, without referring at all to the information of other pixels, and it is possible to obtain a desirable image by preventing missing of image data. Also, by giving an offset beforehand, it is not required to set magnifications of integral multiples for allowing interpolation points and the original pixels to coincide. Therefore, it is possible to provide an image forming apparatus capable of complying with unrounded magnifications other than integral multiples, and capable of reproducing a desirable image even with respect to a character image and a pseudo-halftone image.
It is preferable that the present image forming apparatus includes an affecting section for having a predetermined effect per single interpolation point or per several interpolation points when the interpolation point calculating section calculates interpolation points.
In the image forming apparatus including the affecting section, the offset section gives an offset beforehand and the affecting section has a predetermined effect per single interpolation point and per several interpolation points.
As a result, in the present image forming apparatus, the affecting section affects the offset so that the offset can take various values. As a result, a uniform pattern, which is generated when scaling, is prevented, thus obtaining a desirable image.
It is preferable that the present image forming apparatus includes a correcting section for correcting an interpolation point affected by the affecting section when a result of the effect on the interpolation point exceeds an original referential pixel range.
In the image forming apparatus including the correcting section, in the case where the result of effect on the interpolation points given by the affecting section exceeds the referential original pixel range, the correcting section corrects the interpolation points.
As a result, in the present image forming apparatus, because the offset remains in the referential original pixel range, it is possible to prevent deterioration of image, such as image density falling out of a desirable area.
It is preferable that the present image forming apparatus includes a multi-value restoring section for subjecting an input binary image to multi-value restoration.
In the image forming apparatus including the multi-value restoring section, the multi-value restoring section carries out multi-value restoration with respect to an input binary image.
As a result, in the present image forming apparatus, for scaling of a binary pseudo-halftone image as an image mode, it is possible to carry out scaling after subjecting the image to multi-value restoration in the multi-value restoring section. As a result, it is possible to carry out scaling with ease even for a binary pseudo-halftone image as an image mode.
It is preferable that the present image forming apparatus includes a re-binarizing section for re-binarizing a multi-value image which has been subjected to multi-value restoration and interpolation.
In the image forming apparatus including the re-binarizing section, the image interpolated by the interpolating section by subjecting a binary image to multi-value restoration in the multi-value restoring section is re-binarized by the re-binarizing section.
As a result, in the present image forming apparatus, it is possible to output the scaled image of a multi-value image again as a binary image.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.